A stent is used for applications, for example, an application in which the stent is placed in a stenosed portion or an occluded portion in a tubular organ, such as a bile duct, a ureter, a trachea, a blood vessel, etc., so as to dilate the tubular organ, thereby making bile, blood, or the like easy to flow therethrough, an application in which the stent is placed in a portion where an aneurysm has occurred, so as to prevent the aneurysm from rupturing, or the like.
As the stent, there are exemplified a metallic stent of a cylindrical metal mesh tube, a covered stent in which the outer periphery of a stent body of a cylindrical metal mesh tube is covered by a cover member, a tube stent of a cylindrical resin tube, and the like.
The covered stent and the tube stent have such an advantage that when placed in the tubular organ, invasion of a body tissue into the inside of the stent is readily suppressed.
For example, Patent Literature 1 discloses a covered stent including a cylindrical stent and a cover member provided in the outer peripheral portion of this stent, which is used upon being placed in a body lumen, wherein when the rigidity in the radial direction of the stent is defined as Rfs, the flexural rigidity in the longitudinal axial direction of the stent is defined as Afs, the rigidity in the radial direction of the covered stent is defined as Rfc, and the flexural rigidity in the longitudinal axial direction of the covered stent is defined as Afc, the covered stent satisfies the relationships of (Rfc/Rfs≤1.5) and (Afc/Afs≤2.0), and the cover member is extended by 1.2 to 3.0 times in a diametrically-expanded state along the circumferential direction of the stent.
However, when the stent is placed in a bile conduct, bile is accumulated on the inner surface of the stent, and this is cured to form sludge, such as biliary sludge, etc., so that the stent lumen is readily occlude. In the case of the covered stent or the tube stent, in particular, the stent lumen is readily occluded, and the frequency of replacement by removal and interchange of the stent, or the like increased, so that the load of a patient is liable to increase.
It has been reported that poly(2-methoxyethyl acrylate) (hereinafter also referred to as “PMEA”) is a polymer with low platelet adhesiveness, and PMEA is watched as a biocompatible polymer. Then, PMEA is used upon being coated on the surface of a medical instrument or the like coming into contact with blood.
For example, Patent Literature 2 discloses an implantable device having a coating which includes a polymer selected from the group consisting of poly(2-methoxyethyl acrylate) (PMEA), poly(2-hydroxyethyl acrylate) (PHEA), poly(ethyl acrylate) (PEA), (poly(2-ethylhexyl acrylate) (PEHA), poly(2-phenoxyethyl acrylate) (PPEA), poly(2-ethoxyethyl acrylate) (PEEA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(2-methoxyethyl methacrylate) (PMEMA), poly(ethyl methacrylate) (PEMA), (poly(2-ethylhexyl methacrylate) (PEHMA), poly(2-phenoxyethyl methacrylate) (PPEMA), poly(2-ethoxyethyl methacrylate) (PEEM), and combinations thereof.
Patent Literature 2 describes in paragraph [0030] that: “A stent having the above-described coating is useful for a variety of medical procedures, including, by way of example, treatment of obstructions caused by tumors in bile ducts, esophagus, trachea/bronchi, and other biological passageways. A stent having the above-described coating is particularly useful for treating occluded regions of blood vessels caused by abnormal or inappropriate migration and proliferation of smooth muscle cells, thrombosis, and restenosis. Stents may be placed in a wide array of blood vessels, both arteries and veins. Representative examples of sites include the iliac, renal, and coronary arteries.”